Effect Of Air Mixing On Gas Production Performance Of High-Solids Anaerobic Digestion Of Cow Manure

Air mixing is a kind of biogas fermentation mixing method proposed in recent years,which has dual functions of improving mass transfer and creating transient micro-oxygen environment.At present,the research on air mixing is limited to low concentration biogas fermentation.However,it is not clear whether air mixing is suitable to solve the problems of poor mass transfer and low gas production efficiency in high-solids concentration biogas fermentation.Therefore,this paper took the high-solids biogas fermentation system of cow manure as the research object,studied the effects of different air mixing intensities and methods on the high-solids biogas fermentation of cow manure,determined the optimal air mixing parameters,analyzed the potential of air mixing to improve the gas production performance,and analyzed the material conversion efficiency,microbial community structure,metabolic path and gene function differences,etc.The mechanism of air mixing to improve gas production efficiency is analyzed.The main conclusions are as follows:1.Through the comparative test of high-solids methane fermentation of cow manure under different air mixing intensity,it is determined that 37.5mL /(L min)is the most suitable air mixing intensity.Compared with no mixing,methane production efficiency increased by5.7%,13.1% and 6.3% at the mixing intensity of 12.5,37.5 and 62.5 mL/(L·min),respectively.When the air mixing intensity was 37.5 mL/(L·min),the removal rates of crude fiber and crude fat were the highest,which increased by 10.6% and 12.5%,respectively.The activities of acid protease and α-amylase were increased by 212% and 24.54%,respectively.2.A comparative test on the effects of different mixing methods(air mixing,biogas mixing and no mixing)on the fermentation of high-solids concentration biogas in cow manure was conducted,which further confirmed that air mixing can maximize the gas production performance.Compared with biogas mixing and non-agitation,the methane volume gas yield of air agitation increased by 10.33% and 13.51%,respectively.The maximum contribution rate of the temporary micro-oxygen environment created by air mixing to the increase of methane production was 85.71%,and the contribution rate of mass transfer increased by air mixing was 14.29%.3.Experiments on the effect of air mixing on material transformation at different stages of high-solids concentration biogas fermentation of cow manure showed that air mixing could improve the efficiency of hydrolysis,acid production and acetic acid production.In the hydrolysis and acid production stages,the activity of hydrolyzation-related microorganisms increased by 31.06% and 12.83%,respectively,under the condition of air mixing compared with biogas mixing and no mixing.The production rate of volatile fatty acids(VFA)increased by 9.6% and 58.32%,respectively.The rate of acetic acid production increased by20.59% and 28.96%,respectively.In the methanogenesis stage,there was no significant difference between the experimental group of air mixing and that of non-mixing,indicating that air mixing did not produce significant inhibition on microbial metabolic activity in the methanogenesis stage.4.Based on metagenomic sequencing analysis,the internal mechanism of air mixing promoting the improvement of gas production efficiency was revealed.Air mixing can improve the richness and diversity of microorganisms and have more unique functional genes.In addition,compared with no mixing,the gene abundance of antioxidant enzymes such as superoxide dismutase and catalase was increased,which protected anaerobic bacteria from the damage of reactive oxygen species.The results showed that adding air mixing method could promote metabolic rate and increase methane production.